FIG. 1 shows a known fuel injector arrangement 1 in which a nozzle arrangement 3 is secured to a nozzle holder body 5 by means of a cap nut 7 that is generally U-shaped in cross section. The injector 1 is generally elongate in form and defines a longitudinal axis that runs the length of the injector.
The nozzle arrangement 3 comprises an elongated injection nozzle 9 having an injection region that extends through an aperture 11 in the lower part of the cap nut. The injection nozzle houses an injection needle 13 that is slidable within a bore 15 within the nozzle 13 so as to control fuel delivery though one or more nozzle outlets (not shown in FIG. 1) into a combustion volume (also not shown in FIG. 1).
The needle 13 is supplied with fuel under high pressure from a high pressure fuel inlet 17 and fuel pressure variations within a control volume 19 located on top of the needle 13 control, in use, the movement of the needle 13 to release fuel through the nozzle outlets.
A first distance piece 21 lies above and abuts up against the injection nozzle 9 and includes a through-drilling 23 that serves to convey pressurised fuel from a valve block 25 located adjacent the distance piece to the injection nozzle. The distance piece 21 also includes a blind bore 27 which receives a back end of the injection needle 13 such that the control chamber 19 is defined between the injection needle 13 and the upper end of the blind bore 27.
The valve block 25 is positioned intermediate the distance piece 21 and the nozzle holder body 5 and includes a high pressure drilling 29 that conveys fuel from the high pressure inlet 17 defined in the nozzle holder body to the drilling 23 in the distance piece. The valve block 25 also includes a valve arrangement comprising an elongate valve member 31 and a disc-shaped armature 33 which is acted upon by an actuator arrangement 35.
The actuator arrangement, generally indicated as feature 35 in FIG. 1, is provided within a recess 36 defined in a lower region of the nozzle holder body 5. The actuator arrangement, an electromagnetic solenoid, comprises a magnetic core member 37 and a coil or winding (not shown in FIG. 1) which are used to control the movement of a valve member 31, the position of which affects the pressure within the control volume 19. The valve member 31 is partially provided within a blind bore 39 provided in a lower portion of the actuator arrangement 35. A valve member spring 41 is located within the blind bore 39 and acts to bias the valve 31 away from the actuator arrangement 35.
An upper region of the nozzle holder body includes a lateral recess 43 which receives an electrical connector 45. A bore 47 extends from the recess 43 to the first recess 36 which houses the solenoid 35. An electrical supply lead extends through the bore 47 from the upper face of the solenoid and connects to the electrical connector 45 thereby supplying energy to the solenoid.
The nozzle holder body 5 further includes a high pressure fuel inlet 17 which is defined by a transversely extending port approximately in the mid-region of the nozzle holder body 5. The high pressure fuel inlet is conically re-entrant in shape to receive an inlet of the so-called “lance” type which is clamped into this inlet. The fuel injector defines a conical seating surface which is shaped for engagement with a high pressure fuel supply connector, in use. An oblique drilling 49a, 49b extends from the inlet 17 into the nozzle holder body 5 and then angles downward in a direction to connect to the high pressure drilling 29 defined in the valve block 25.
It is noted that in the vicinity of the actuator arrangement 35 the drilling is at an angle to the longitudinal axis of the fuel injector 1. It can further be seen that the angle with respect to the longitudinal axis changes as the drilling 49b connects to the high pressure drilling 29 in the valve block 25. This change of direction of the drillings 49b/29 is necessary in order for the drillings to avoid components within the injector, especially the solenoid actuator. However, it is noted that this arrangement results in high stresses at the various intersections within the injector, this is increasingly so, in sympathy with increasing changes in angle at the intersection.
It is further noted that the second part of the drilling 49b is substantially vertical in the arrangement shown in FIG. 1. This is because in order to maximise the cross-section of the nozzle holder body available for the solenoid actuator (and hence its performance) in the region of the solenoid actuator, a near vertical drilling here (past the solenoid actuator) is the option that takes up least cross-sectional area in this region.
It is also noted that within the nozzle holder body 5 the drilling 49a/49b changes direction at intersection point X. Point X represents the intersection of two drillings (49a, 49b) into the body 5, the first of which (49a) is made from the inlet 17 and the second of which (49b) is made from the bottom face of the body 5 (i.e. from the face that abuts valve block 25.
It is noted that the presence of these two intersecting drillings raises a number of disadvantages. The formation of the drillings requires a high level of accuracy to ensure the two drillings actually intersect. Furthermore, the drillings which are formed leave sharp edges at the intersection A which needs to be smoothed (e.g. using a sand or grit impregnated putty). Finally, the presence of a change in direction at intersection point X results in stress raisers.
The cap nut 7 houses the injection nozzle 9, the distance piece 21 and the valve arrangement 31, 33 and engages the nozzle holder body 5 by means of a screw thread.
FIG. 2 shows an enlarged view of a known actuator arrangement 35 in which like numerals between FIGS. 1 and 2 have been used to denote like features.
It is noted that the magnetic core material 37 is surrounded by a coil 50. A coil-former or bobbin 52 supports the coil 50 and lies between the coil 50 and the core member 37. A pole piece 53 is provided with a bore 54 within which the coil 50, bobbin 52 and core member 37 are located. The pole piece, coil 50 and core member 37 together form the stator part of a “magnetic circuit” within the actuator arrangement 35.
The core member 37 and pole piece 53 are both constructed of a soft magnetic material namely iron and it is noted that the core member 37 forms the inner part of the magnetic circuit (since part of the member 37 is formed within the coil 50) and the pole piece 53 forms the outer part of the magnetic circuit (it is formed outside the coil 50).
The core member 37 is generally T-shaped in cross section along its longitudinal axis (which is parallel with the longitudinal axis of the fuel injector 1) and comprises a central axial portion 55 and a horizontal top portion 56 (the “top” of the “T”). The bobbin 52 and coil 50 surround the axial portion 55. It is noted that the top portion 56 is stepped in two places (57, 58) and the second stepped portion forms a shoulder 58 which is arranged to abut a top face 60 of the pole piece 53 when the actuator arrangement 35 is assembled.
It is noted that the arrangement depicted in FIG. 2 is not yet assembled as there is a gap between the second shoulder 58 and the top face 60.
The known assembly method of the actuator arrangement of FIG. 2 comprises the following steps:    i) moulding the bobbin 52;    ii) winding the wire coil 50 onto the bobbin 52. It is noted that the bobbin 52 needs to be strong enough to survive the winding, handling and production processes. This therefore necessitates a relatively thick insulating wall of the order of 0.35 mm. Additionally, there will need to be some clearance between the bobbin 52 and the axial portion 55 of the inner core member 37.    iii) introduce the wound bobbin 52 over the axial portion 55 of the inner core member 37;    iv) introduce the inner core member 37, bobbin 52 and coil 50 into the bore of the pole piece 53 until the shoulder 58 abuts the top face 60 of the pole piece 53. It is noted that the stepped portion 57 of the core member 37 is of complementary shape to the bore 54 of the pole piece 53.
Correct assembly of the actuator arrangement requires the various components of the arrangement to be constructed to within specific tolerances. Known problems with the above arrangement and assembly method as a result of unfavourable tolerance build-ups are the failure of the bobbin 52 to form a seal with the lower portion 62 of the pole piece 53, thereby letting encapsulant past this point, and the crushing of the bobbin 52 as it is inserted into the bore 54. The coil also needs to be sealed away from the inner face of the pole piece 53.
It is noted that there is pressure on manufacturers, for example from a need to meet emissions regulations, to make engines which are smaller, lighter and more economical.
In sympathy, there is also pressure on Fuel Injection Equipment (FIE) manufacturers to make FIE engines which are smaller, lighter and more economical, including injectors of smaller diameters.
It is therefore an object of the present invention to provide an actuator arrangement that overcomes or substantially mitigates the above problems.